> > I am trying to instrument linux-2.2.19 kernel to measure the number of > > times each page is read. That is, for each page that is read by each > > process from disk, there should be a counter. Once the measurement started, > > the number of times a page is read from disk by a process should be counted; > > if page is written out to swap space and brought back in, this should be > > included in the count. > > All swap and mmapped pages are already associated with disk > locations in the kernel, via the address_space structure. > However, when a page is evicted from RAM, naturally its > "identity" is destroyed. You would need to keep a list or > array of mappings between file offsets (or swap id) and > read count. Attaching such to the address_space struct is > probably the sensible thing to do. You could then manage > the read count in the swap.c code when a page is read in > from disk. Though disk readahead might cause you some > problems - do you count all reads, or only those initiated > to service page faults? I want to count all reads, such as reading inodes. In this case, I may have to look into "ll_rw_block()", since this routine is used for all disk I/O activities, including those not involving swapping. But, at that level, I only know the block no. How can I still associate to a block reads to a virtual address? And, can a block read be interpreated as a page read?(because, as far as I saw for ext2 fs, one block is usually 4k) > Much simpler to do the accounting in the kernel and provide a > /proc interface to get the data, I think. Good idea. I may go and try. > > That's why I am here to ask you to give me some > > suggestions. The aim is just to measure the number of each page is read when > > runing a process. > > > > Btw, is it feasible to use or introduce some additional bits in process > > page-table to accomplish this? > > I think that would be enormously more trouble than it's worth, and > not possible anyway on many platforms. Also, remember that only a Why is it so troublesome by modifying page-table? > small percentage of page faults require disk reads; the > majority are serviced from the page cache (under normal conditions). > So tracking the number of per-process faults would not tell you > much about disk activity. But, when the memory size is small, it must increase the disk activity for a single process tremendously. Thanks for you suggestions! -- Cheers! Zou Min zoum@comp.nus.edu.sg ----------------------------------------------------------------------------- To attract a vegetarian, make a noise like a wounded vegetable. - Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ IRC Channel: irc.openprojects.net / #kernelnewbies Web Page: http://www.kernelnewbies.org/
